Since the Kyoto Protocol on the reduction of carbon dioxide emissions has entered into force globally since 2005 due to the seriousness of global warming, there have been various studies on the efficient utilization of carbon dioxide, as well as the development of technologies to reduce carbon dioxide emissions.
As a technology to utilize carbon dioxide, a method has been studied, in which synthesis gas is produced by performing steam and carbon dioxide reforming of natural gas (SCR) and useful chemical raw materials (e.g., methanol, dimethyl ether, etc.,) are produced by using the synthesis gas as a raw material.3CH4+2H2O+CO2→8H2+4CO ΔH=712 KJ/mol  SCR:CO+2H2→CH3OH ΔH=−90 KJ/mol  Methanol synthesis:CO2+3H2→CH3OH+H2O ΔH=−49.6 kJ/mol
U.S. Pat. No. 6,100,303 discloses a method for achieving reduced construction cost of a process and improved energy efficiency by using combustion type and heat exchanger type reformers which are two different types of reformers in a steam reforming process of natural gas and using some (purge gas) of unreacted gas as a raw material for reforming/methanol synthesis units and also as the fuel gas of the reformer, as a method for improving energy efficiency and CO2 utilization.
Further, U.S. Pat. No. 6,218,439 discloses a process for minimizing an emission amount of CO2 by re-inputting CO2 formed during steam reforming process into the reformer or methanol synthesis reactor after separation process as a utilization scheme of CO2 generated during the reaction.
However, a natural gas reforming method and a recycling method, which are presented in the above patents, are different from the methods used in the present invention. In particular, a layout of a heat exchanger used in the present invention is never disclosed.